From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0BE7C433ED for ; Thu, 22 Apr 2021 15:28:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B636D61458 for ; Thu, 22 Apr 2021 15:28:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236548AbhDVP3K (ORCPT ); Thu, 22 Apr 2021 11:29:10 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:16151 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233106AbhDVP3G (ORCPT ); Thu, 22 Apr 2021 11:29:06 -0400 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4FR1T26DV9zpZmV; Thu, 22 Apr 2021 23:25:26 +0800 (CST) Received: from [10.174.177.244] (10.174.177.244) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.498.0; Thu, 22 Apr 2021 23:28:24 +0800 Subject: Re: [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid() To: Mike Rapoport CC: , Andrew Morton , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , David Hildenbrand , Marc Zyngier , "Mark Rutland" , Mike Rapoport , "Will Deacon" , , , References: <20210421065108.1987-1-rppt@kernel.org> <9aa68d26-d736-3b75-4828-f148964eb7f0@huawei.com> From: Kefeng Wang Message-ID: <33fa74c2-f32d-f224-eb30-acdb717179ff@huawei.com> Date: Thu, 22 Apr 2021 23:28:24 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.174.177.244] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/4/22 15:29, Mike Rapoport wrote: > On Thu, Apr 22, 2021 at 03:00:20PM +0800, Kefeng Wang wrote: >> On 2021/4/21 14:51, Mike Rapoport wrote: >>> From: Mike Rapoport >>> >>> Hi, >>> >>> These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire >>> pfn_valid_within() to 1. >>> >>> The idea is to mark NOMAP pages as reserved in the memory map and restore >>> the intended semantics of pfn_valid() to designate availability of struct >>> page for a pfn. >>> >>> With this the core mm will be able to cope with the fact that it cannot use >>> NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks >>> will be treated correctly even without the need for pfn_valid_within. >>> >>> The patches are only boot tested on qemu-system-aarch64 so I'd really >>> appreciate memory stress tests on real hardware. >>> >>> If this actually works we'll be one step closer to drop custom pfn_valid() >>> on arm64 altogether. >> Hi Mike，I have a question, without HOLES_IN_ZONE, the pfn_valid_within() in >> move_freepages_block()->move_freepages() >> will be optimized, if there are holes in zone, the 'struce page'(memory map) >> for pfn range of hole will be free by >> free_memmap(), and then the page traverse in the zone(with holes) from >> move_freepages() will meet the wrong page， >> then it could panic at PageLRU(page) test, check link[1], > First, HOLES_IN_ZONE name us hugely misleading, this configuration option > has nothing to to with memory holes, but rather it is there to deal with > holes or undefined struct pages in the memory map, when these holes can be > inside a MAX_ORDER_NR_PAGES region. > > In general pfn walkers use pfn_valid() and pfn_valid_within() to avoid > accessing *missing* struct pages, like those that are freed at > free_memmap(). But on arm64 these tests also filter out the nomap entries > because their struct pages are not initialized. > > The panic you refer to happened because there was an uninitialized struct > page in the middle of MAX_ORDER_NR_PAGES region because it corresponded to > nomap memory. > > With these changes I make sure that such pages will be properly initialized > as PageReserved and the pfn walkers will be able to rely on the memory map. > > Note also, that free_memmap() aligns the parts being freed on MAX_ORDER > boundaries, so there will be no missing parts in the memory map within a > MAX_ORDER_NR_PAGES region. Ok, thanks, we met a same panic like the link on arm32(without HOLES_IN_ZONE), the scheme for arm64 could be suit for arm32, right?  I will try the patchset with some changes on arm32 and give some feedback. Again, the stupid question, where will mark the region of memblock with MEMBLOCK_NOMAP flag ? > >> "The idea is to mark NOMAP pages as reserved in the memory map", I see the >> patch2 check memblock_is_nomap() in memory region >> of memblock, but it seems that memblock_mark_nomap() is not called(maybe I >> missed), then memmap_init_reserved_pages() won't >> work, so should the HOLES_IN_ZONE still be needed for generic mm code? >> >> [1] https://lore.kernel.org/linux-arm-kernel/541193a6-2bce-f042-5bb2-88913d5f1047@arm.com/ >>